CINCINNATI - After playing 18 innings and more than six hours of baseball on Saturday, it was a pair of firsts which capped off the Milwaukee Brewers' first doubleheader sweep in two seasons.

Left fielder Shane Peterson hit his first career home run and right-hander Ariel Pena earned his first big-league victory in the Brewers' 7-3 victory over the Cincinnati Reds at Great American Ball Park.

"It was a long day, but a good day," said manager Craig Counsell. "We played well."

The big blow was provided by third baseman Elian Herrera, who hit a three-run homer in the ninth off Jumbo Diaz to seal Milwaukee's sixth straight win.

Herrera also homered in the Brewers' 8-6 win in the first game on Saturday.

"We've been playing better," said Herrera. "We've been getting the big hit. I've not been worrying too much, just focusing every at bat."

After Friday's regularly scheduled game was postponed because of rain, Saturday's nightcap also was delayed one hour and 33 minutes in the third inning.

Pena (1-0) picked up the victory in his major-league debut, allowing two earned runs in three innings of relief. Starter Wily Peralta worked two scoreless innings before the rain.

"Like any first time out, it took him time to settle in the game," said Counsell. "We didn't want to send Wily back out there. (The rain delay) was too long."

Pena had the lineup card and baseball from his milestone win stored in his locker following the game.

"I'm a little excited," Pena said, smiling. "It wasn't too difficult (coming in after long rain delay). Yes, this is the big leagues. But I didn't feel any pressure at all."

It was the first doubleheader sweep for Milwaukee (60-75) since July 30, 2013, against the Cubs at Wrigley Field.

Left fielder Adam Duvall hit his second career homer for Cincinnati (55-79), which dropped to 6-9 against the Brewers this season.

Rookie right-hander Keyvius Sampson (2-3) took the loss for the Reds. His last victory came four starts ago on August 13.

"It's mostly my head falling off (to one side)," Sampson said. "If your head's falling off, your body's going to go with your head. I need to try to keep my head going straight to the plate."

Reds center fielder Ryan LaMarre got Sampson off the hook in the first inning when he made an over-the-shoulder catch of shortstop Jean Segura's bases-loaded drive for the third out.

Sampson allowed two hits and walked two in 23 pitches in the first inning.

With light rain falling in the third, RBI singles by right fielder Domingo Santana and Peterson put Milwaukee ahead 2-0.

The Brewers led 3-0 in the third when the game was delayed by a heavy thunderstorm.

When the rain subsided, Pena came out of the bullpen to make his big-league debut in relief of Peralta, who had thrown only 39 pitches.

Sampson exited as well after allowing three earned runs and three walks in three innings.

"It's just been a struggle for him to get ahead and stay ahead in the count," Reds manager Bryan Price said. "That makes a big difference. When he was going good, he was clustering pitches in the zone. Now he's spraying them all around. That usually doesn't lead to success."

His replacement - right-hander Pedro Villarreal - made Milwaukee pay for issuing an intentional walk before facing him in the fourth by lacing a double to center to make the score 3-2. It was Villarreal's first career double and RBI.

But Peterson took Villarreal deep in the sixth.

"Petey's been looking for a home run," Counsell said. "He was wondering if it was going to come. Not sure if you could see the dugout. They were thrilled for him."

NOTES: Brewers RHP Matt Garza made his last start of the season in the first game of Saturday's doubleheader, allowing five runs in 4 2/3 innings in an 8-6 win over the Reds. Brewers GM Doug Melvin told reporters that Garza was informed earlier in the week he was being shut down and declined an offer to move to the bullpen. Garza finished 6-14 with a 5.63 ERA in 26 appearances, including one in relief. ... Reds 1B Joey Votto extended his hitting streak to eight games with a first-inning single. ... Home plate umpire Will Little left in the third inning because of a family medical issue and was replaced behind home plate by Phil Cuzzi. ... The Reds have had 16 rain delays at home this season totaling 23 hours, 19 minutes.